1. Field of the Invention
Aspects of the present invention relate to an electron emission device, an electron emission display apparatus having the electron emission device, and a method of manufacturing the electron emission device, and more particularly, to an electron emission device having a structure in which a voltage applied to an electron emission source is uniformly distributed, an electron emission display apparatus having the electron emission device to increase brightness uniformity of pixels, and a method of manufacturing the electron emission device.
2. Description of the Related Art
Generally, electron emission devices use a thermal cathode or a cold cathode as an electron emission source. Electron emission devices that use a cold cathode as an electron emission source include field emission device (FED) type devices, surface conduction emitter (SCE) type devices, metal insulator metal (MIM) type devices, metal insulator semiconductor (MIS) type devices, ballistic electron surface emitting (BSC) type devices, etc.
An FED type electron emission device uses the principle that when a material having a low work function or a high β function is used as an electron emission source, the material readily emits electrons in a vacuum due to an electric potential. Devices that employ a tapered tip structure formed of, for example, Mo or Si as a main component, a carbon group material such as graphite, diamond like carbon (DLC), etc., or a nano structure such as nanotubes, nano wires, etc., have been developed. Typically FED type electron emission devices comprise an array of electron emitters, in which case they may be referred to as field emitter array (FEA) devices.
In an SCE type electron emission device, an electron emission source includes a conductive thin film having micro cracks between first and second electrodes facing each other on a substrate. The electron emission device makes use of the principle that electrons are emitted from the micro cracks, which are electron emission sources, when a current flows on the surface of the conductive thin film by applying a voltage between the electrodes.
MIM and MIS type electron emission devices, that is, devices that have a metal-dielectric layer-metal (MIM type) structure or a metal-dielectric layer-semiconductor (MIS type) structure, make use of the principle that when voltages are applied to two metals having a dielectric layer therebetween or to a metal and a semiconductor having a dielectric layer therebetween, electrons migrate from the metal or the semiconductor having a high electron potential to the metal having a low electron potential.
A BSE type electron emission device includes an electron emission source making use of the principle that electrons travel without scattering when the size of a semiconductor is smaller than the mean-free-path of electrons in the semiconductor. To form the electron emission source, an electron supply layer formed of a metal or a semiconductor is formed on an ohmic electrode, and an insulating layer and a metal thin film are formed on the electron supply layer. When a voltage is applied between the ohmic electrode and the metal thin film, the electron emission source emits electrons.
FEA type electron emission devices can be classified into top gate devices and bottom gate devices according to the location of a cathode electrode and a gate electrode, and can be classified as diodes, triodes, tetrodes, etc., according to the number of electrodes they include. An example of a display device that uses an FEA type electron emission device is depicted in FIGS. 1 and 2.
FIG. 1 is a partial perspective view of a conventional top gate type electron emission display device 100, and FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.
Referring to FIGS. 1 and 2, the conventional electron emission display device 100 includes an electron emission device 101 and a front panel 102, which are located parallel to each other and form a vacuum light emitting space 103, and a spacer 60 that maintains a gap between the electron emission device 101 and the front panel 102.
The electron emission device 101 includes a first substrate 110, a plurality of gate electrodes 140 and a plurality of cathode electrodes 120 crossing the gate electrodes 140 on the first substrate 110, and an insulating layer 130 which is located between the gate electrodes 140 and the cathode electrodes 120 and electrically insulates the gate electrodes 140 from the cathode electrodes 120.
A plurality of electron emission source holes 131 are formed on regions where the gate electrodes 140 cross the cathode electrodes 120. An electron emission source 150 is formed in each of the electron emission source holes 131.
The front panel 102 includes a second substrate 90, an anode electrode 80 located on the lower surface of the second substrate 90, and a plurality of phosphor layers 70 located on the lower surface of the anode electrode 80.
A display device that displays an image using an FEA type electron emission device often has non-uniform brightness. In addition, since the distances between the gate electrode and tips of a carbon nanotube (CNT) in each electron emission source are not uniform, current density is reduced and uniform brightness cannot be obtained. The non-uniformity in brightness between pixels greatly impairs the quality of the image, and thus, should be prevented.